5 answers

Many factors might impact max concurrency such as controllers' CPU clock speed, the cluster size and network topology. There is max concurrency cap for any given environment. Capacity planning and CLI/API call retry are recommended best practices.

Are you looking to cap the number? you just find out if there is a limit.
Either way no, the limit is going to be the physical resources to your environment. In my personal testing in a small 3 node environment, I was able to launch upwards of 120 small vms at once.

What you will see when you reach the limit of your systems is some instances will fail to launch, while the rest launch this tells you that a needed resource was not available during the spawning phase.